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Posted on Dec 15, 2020
Cast iron is a 2 wt. percent-4 wt. percent carbon, 1 wt. percent-3 wt. percent silicon and lesser quantities of minor components iron alloy. In contrast, steel has a lower carbon content and a lower silicon content of up to 2 percent by weight. By alloying with limited amounts of manganese, molybdenum, cerium, nickel, copper, vanadium, and titanium before being cast, cast iron can also be further optimized.
Cast iron is a 2 wt. percent-4 wt. percent carbon, 1 wt. percent-3 wt. percent silicon and lesser quantities of minor components iron alloy. In contrast, steel has a lower carbon content and a lower silicon content of up to 2 percent by weight. By alloying with limited amounts of manganese, molybdenum, cerium, nickel, copper, vanadium, and titanium before being cast, cast iron can also be further optimized. It is known as either white cast iron or grey cast iron based on the silicon content of the cast iron and can be further processed under specific temperatures to create malleable or ductile cast iron.
:: Read More: Introduction to Cast Iron Casting
Cast iron is strongly favored for its capacity to be easily cast into complicated forms when molten and for its low quality. In addition, its properties can be easily altered by adjusting the composition and cooling rate without significant changes to manufacturing processes. Its other main advantages over cast steel are quick machining, vibration dampening, compressive strength, wear resistance, and corrosion resistance. The corrosion resistance of cast iron is strengthened by the addition of minor elements such as silicon, nickel, chromium, molybdenum, and copper.
Cast iron can be classified as grey cast iron, white cast iron, malleable cast iron, and ductile cast iron depending on its composition. Cast iron grey has a dark grey fracture color due to a graphitic microstructure, grey cast iron, or gray iron. The presence of graphite flakes is due to the inclusion of silicon, which as opposed to iron carbide, helps to stabilize carbon in the form of graphite. Typically, grey cast iron has a composition of 2.5 wt. percent-4.0 wt. carbon percent and 1.0 wt. percent-3.0 wt. silicon percent.
The most common color of cast iron is grey. It is used in applications such as internal combustion engine cylinder blocks, flywheels, gearbox cases, manifolds, disk brake rotors, and cookware, where its high rigidity, machinability, friction dampening, high heat power, and high thermal conductivity are beneficial. The ASTM International standard A48 is a widely used classification for grey cast iron. Gray cast iron is rated according to its tensile strength under this scheme, with category 20 gray cast iron, for example, having a minimum tensile strength of 20,000 psi (140 MPa).
Because of the presence of iron carbide, or cementite Fe3C, white cast iron has a white fracture color. As contrasted to graphite, the presence of carbon in this form is the result of a lower content of silicon relative to grey cast iron. Usually, white cast iron includes 1.8 wt. percent-3.6 wt. percent biomass, 0.5 wt. percent-1.9 wt. Percent silicon and 1.0 wt.% – 2.0 wt.% manganese. White cast irons are highly wear-resistant and delicate. As a consequence of their microstructure containing massive iron carbide fragments, they show high hardness and are not readily machined.
In abrasion-resistant sections where brittleness is of limited importance, such as shell liners, slurry pumps, ball mills, lifter bars, extrusion nozzles, cement mixers, pipe fittings, flanges, crushers, and pump impellers, white cast iron is used. High chrome white iron, ASTM A532, is a typical grade of white iron. This includes nickel and chromium for strong abrasion applications with low effect.
Via a slow annealing heat treatment of white cast iron, malleable cast irons are formed. This results in the conversion of carbon into graphite in the form of iron carbide into white iron, with ferrite or pearlite being composed of the remaining matrix. In the type of circular or nodular shapes, graphite is present. Strong malleability and good ductility are demonstrated by malleable cast iron. It exhibits strong crack durability at low temperatures due to the decreased silicon content relative to other cast iron.
Malleable cast iron is used for electrical fittings and machinery, hand tools, pipe fittings, washers, brackets, agricultural equipment, construction hardware, and machine parts, owing to its high tensile strength and ductility. The ASTM A47 is a common classification for malleable cast iron.
The existence of graphite in the form of spherical nodules, as with malleable cast iron, is characterized by ductile cast iron, also known as nodular cast iron and spheroidal graphite cast iron. Unlike malleable cast iron, ductile cast iron is formed by particular chemical composition, not by heat treatment of white iron. 3.2 wt. percent-3.6 wt. percent carbon, 2.2 wt. percent-2.8 wt. percent silicon and 0.1 wt. percent-0.22 wt. percent of manganese, as well as lower concentrations of magnesium, arsenic, copper, and sulfur, the spherical structure of the graphite inclusions, is responsible for the existence of manganese.
This steel is more ductile than grey or white cast iron because of its microstructure. It is used as a ductile iron conduit for water and sanitation infrastructure for this purpose. It is also capable of withstanding thermal cycling and is also used in gears and suspension modules for automobiles, brakes and valves, pumps and hydraulic parts, and wind turbine housings. ASTM A536 is generally known as ductile cast iron.
Iron must be removed from iron ore in order to manufacture cast iron. In a blast furnace, the ore is smelted where it separates into pig iron and slag. The furnace is heated in an oxygen atmosphere to about 1800 degrees Celsius and the slag produced rises to the surface and can be removed. The molten pig iron produces carbon of about 3 wt. percent-5 wt. percent. Then the iron, coal, coke, and limestone are mixed with this. The carbon content is lowered until impurities are separated selectively from this iron. In order to transform the carbon content to graphite or cementite, silicon may be added at this stage. After that, the iron is cast into different shapes and this is white cast iron.
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